An Israeli soldier directs a Merkava tank at an army deployment area near the border with Gaza.

An Israeli soldier directs a Merkava tank at an army deployment area near the border with Gaza.

Photo: Menahem Kahana, AFP/Getty Images

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Mourners carry a Palestinian boy, one of three children killed by an Israeli missile strike in Gaza City.

Mourners carry a Palestinian boy, one of three children killed by an Israeli missile strike in Gaza City.

Photo: Hatem Moussa, Associated Press

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The mother, left, of Fullah Tariq Shahebar, 8, one of three children who were killed in an Israeli missile strike earlier, is comforted by a woman after she identified her daughter at the hospital's morgue, in Gaza City, Thursday, July 17, 2014. The children were killed by an Israeli missile strike at their house feeding pigeons on their roof in the Sabra neighborhood of Gaza City, the family said. Fierce fighting between Israel and Hamas resumed Thursday, including an airstrike that killed three Palestinian children feeding pigeons on their roof, after a temporary cease-fire that allowed Gazans to stock up on supplies. (AP Photo/Hatem Moussa) less

The mother, left, of Fullah Tariq Shahebar, 8, one of three children who were killed in an Israeli missile strike earlier, is comforted by a woman after she identified her daughter at the hospital's morgue, in ... more

Photo: Hatem Moussa, Associated Press

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Israel bombards Gaza Strip in ground invasion

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Gaza City, Gaza Strip --

The heavy thud of tank shells, often just seconds apart, echoed across the Gaza Strip early Friday as thousands of Israeli soldiers launched a ground invasion, escalating a 10-day campaign of heavy air bombardments to try to destroy Hamas' rocket-firing abilities and the tunnels militants use to infiltrate Israel.

The Israeli military reported one soldier killed in the ground offensive. The details were not available.

Flares lit up the night sky before dawn and the wail of ambulance sirens mixed with the Muslim call to prayer from mosque loudspeakers as thick smoke rose into the air from sites where shells and missiles struck.

"There is a tank shell every minute," said an official in the Gaza security operations room, who said all of the seaside strip's border areas were being shelled and that Hamas fighters were exchanging fire with Israeli troops near a northern Gaza town.

"There is also fire from the sea toward police checkpoints."

Israel launched the offensive late Thursday after becoming increasingly exasperated with rocket fire from Gaza on its cities, especially following Hamas' rejection of an Egyptian cease-fire plan earlier in the week. Palestinian militants have fired more than 1,500 rockets at Israeli cities since fighting began.

However, a ground offensive could quickly lead to military and political entanglements for Israel, especially if more Palestinian civilians are killed.

More than 240 Palestinians have already died in the air campaign, including 14 children under age 12 killed over the past two days, according to Palestinian health officials. One Israeli has also died.

Israel accuses Hamas of firing from within populated neighborhoods and using civilians as "human shields."

Hamas struck a defiant tone. A spokesman, Fawzi Barhoum, said Israel "will pay dearly" for the assault. "Hamas is ready for a confrontation," he said.

The Israeli operation began around 10 p.m. Thursday, with what the military said was an open-ended assault to be carried out on several fronts.

"Large ground forces accompanied by massive air force support, naval forces and intelligence, are taking over targets in Gaza, operating against tunnels and terror activists and infrastructure," said chief military spokesman Brig. Gen. Motti Almoz.

He called on Gaza residents to evacuate targeted areas, warning the "military is operating there with very great force."

Israel had called up 48,000 reserve soldiers, and the Cabinet Thursday authorized the military to call up 18,000 more, the military said.